Input devices, in particular capacitive input devices, with strip-shaped input areas are well known in the technical field, e.g. from document U.S. Pat. No. 4,264,903. The latter discloses a strip-shaped capacitive touchpad, comprising a solid panel having a front surface facing an operator of the touchpad and a rear surface facing away from the operator, a plurality of detection electrodes disposed along a predefined geometric curve (e.g. a straight line or an annular curve) and applied to the rear surface of the panel. The emplacement of the operator's finger on the front surface of the panel at a point upon the detection electrode pattern causes an additional capacitance between a pair of adjacent detection electrodes or one detection electrode and ground, which can be measured and which the position of the operator's finger can be derived from. The detection electrodes are shown as being interdigitated with the respective neighbouring detection electrode or detection electrodes.
To move a cursor (also referred to as a pointer) or another visual indicator on a display screen associated to a touchpad, the user puts his or her finger on the operating surface (the surface corresponding to the input area of the touchpad, which is, in the above example on the front surface of the panel) and then slides the finger while keeping it in light touch with the operating surface. In laptop computers and other electronic appliances, touchpads are often associated with one or more buttons, which provide mouse-click functionality, e.g. for selecting a displayed object currently highlighted or pointed at on the display, drag-dropping a displayed object (by positioning the cursor or visual indicator on the object to be dragged, pressing the button and keeping
the button pressed while moving the cursor to the desired location, then releasing the button for “dropping” the object), etc. The disadvantage of separate buttons is that the user needs both his or her hands to access the mouse-click functionality. Indeed, the user usually depresses the button with the forefinger of one hand while moving the cursor with the forefinger or the middle finger of the other hand.
In certain touchpads, such mouse-click functionality can also be emulated by tapping the operating surface with the finger. Document U.S. Pat. No. 5,907,327 describes that touchpads with such “tapping” function, make it possible with one finger to perform not only the above-mentioned “single-click” operations (selecting, dragging, etc.) but also “double-click” operations (opening a folder, starting an application, etc.). Dragging can be carried out on a touchpad by first putting the cursor upon the displayed object to be dragged (e.g. an icon or window), then tapping the input area surface once, placing the finger on the input area surface immediately after the tapping and sliding the finger on the surface, thereby causing the cursor to move on the screen. Some touchpads even provide for the so-called drag-lock functionality, so that the finger may be lifted from the input area surface (e.g. when reaching the border of the input area) without causing the touchpad to leave the dragging mode. The touchpad may, in particular, be configured to go into drag-lock mode if the user's finger has been moved a predefined minimum distance after the touchpad had been placed into dragging mode.
While some people have no difficulty in using the tapping functionality provided by touchpads, others deliberately switch it off (if this is possible and if they know how this can be done) and work with the associated buttons or keys because they otherwise would often unintentionally trigger the tapping functionality. Accordingly, there is still room for making touchpads user-friendlier. In this regard, differentiation between intentional and unintentional user action is of particular concern.
Document U.S. Pat. No. 6,424,338 mentions that mouse-clicks can be implemented by a switch responsive to downward pressure, positioned underneath a touch pad surface. Document US 2006/0232559 A1 discloses a capacitive touchpad with a physical key function, comprising a soft flexible first conductive layer, a second conductive layer and a soft flexible insulator layer disposed between the first and second conductive layers. The insulator layer has holes therein for the first conductive layer to connect to the second conductive layer while the touchpad is pressed and to thus trigger a predetermined key function.